Effectiveness of television advertising can be measured, somewhat, by broadcasting (sometimes in a loud voice) the message to “call now” so that interested parties will immediately make a phone call. However, such responses would likely be limited to those with an immediate interest in what is being sold and exclude those who are undecided about the offering, do not have immediate access to a telephone, etc., but might nonetheless be influenced by the advertising.
With the advent of Internet-based advertising (here, the “Internet” is used as just one example of a network over which many people can participate in many roles), other techniques have been developed for determining effectiveness of Internet ads, such as through the use of banner ads wherein the URL that is requested when a viewer clicks on the ad is a URL that first calls to an ad tracking server and then is passed on to another URL that provides the view with additional information. When the system providing the ad is the same as the one measuring response, the measuring might be simple. However, it is more complicated when there is not a direct connection.
A well-known adage, which some attribute to John Wanamaker (1832-1922), a department store merchant, is that “Half the money I spend on advertising is wasted; the trouble is I don't know which half.” This has spurred advertisers to be more focused, so as to increase advertising effectiveness, but also to limit advertising so that it goes to interested consumers rather than to disinterested consumers.
Some approaches to advertising effectiveness rely on gathering large amounts of data on individual consumers and targeting advertisements to each of them. This is often disliked by consumers, who might not want individual details maintained on them, and still possibly seeing irrelevant advertising. This can also require inordinate amounts of effort on the part of advertisers in dealing with individual messages to each potential consumer.